Tuning the interactions between electron spins in fullerene-based triad systems

Abstract

SummaryA series of six fullerene–linker–fullerene triads have been prepared by the stepwise addition of the fullerene cages to bridging moieties thus allowing the systematic variation of fullerene cage (C60 or C70) and linker (oxalate, acetate or terephthalate) and enabling precise control over the inter-fullerene separation. The fullerene triads exhibit good solubility in common organic solvents, have linear geometries and are diastereomerically pure. Cyclic voltammetric measurements demonstrate the excellent electron accepting capacity of all triads, with up to 6 electrons taken up per molecule in the potential range between −2.3 and 0.2 V (vs Fc+/Fc). No significant electronic interactions between fullerene cages are observed in the ground state indicating that the individual properties of each C60 or C70 cage are retained within the triads. The electron–electron interactions in the electrochemically generated dianions of these triads, with one electron per fullerene cage were studied by EPR spectroscopy. The nature of electron–electron coupling observed at 77 K can be described as an equilibrium between doublet and triplet state biradicals which depends on the inter-fullerene spacing. The shorter oxalate-bridged triads exhibit stronger spin–spin coupling with triplet character, while in the longer terephthalate-bridged triads the intramolecular spin–spin coupling is significantly reduced.

Linking Deltahedral Zintl Clusters with Conjugated Organic Building Blocks: Synthesis and Characterization of the Zintl Triad [R‐Ge9‐CHCHCHCH‐Ge9‐R]4−

“…Such complex molecules are promising candidates for electron-transfer systems, and the electronic interactions between two C 60 units has been the subject of different studies. [1,2] As pointed out earlier, C 60 molecules show a close relationship to homoatomic deltahedral Zintl ions of Group 14 elements [E m ] nÀ (E = Si, Ge, Sn, Pb; m = 9, 10, 12). [3] Both kinds of basic polyhedral building units feature delocalized electronic systems such as the conjugated p electrons in the former case and an electron-deficient bonding system, according to Wades rules, which can also be considered as resonance-delocalized s bonds (spherical aromaticity), [4] in the latter.…”

“…[15][16][17][18][19] Whereas many of these products are only available in rather low yields, the vinylation of [Ge 9 ] 4À by bis(trimethylsilyl)acetylene in ethylenediamine leads to good quantities of the bis-vinylated clusters [Ge 9 -(CH = CH 2 ) 2 ] 2À [17] besides minor amounts of mono-and, in that case, even tris-vinylated species, [Ge 9 -(CH = CH 2 )] 3À and [Ge 9 -(CH = CH 2 ) 3 ] À , respectively. [15,16] Although it is obvious to link such [Ge 9 -(CR= CHR) n ] (4Àn)À (n = 1-2) species via their olefinic substituents, [20] as successfully applied for fullerenes, [1] such reactions have not been reported to date.…”

Stabilising the lowest energy charge-separated state in a {metal chromophore – fullerene} assembly: a tuneable panchromatic absorbing donor–acceptor triad

“… 55 The intense central feature is assigned to an organic radical formed as a result of decomposition of the sample and has been observed previously in bulk electrolysis experiments of solutions containing fullerene. 56 We were not able to determine the nature of the 4 th reduction process due to the low stability of the multi-electron reduced species.…”

CF2‐Bridged C60 Fullerene Dimers and their Optical Transitions

“…Fullerene dimers have been synthesized by utilizing various bridging groups that link the two buckyballs. A wide range of methods can be found in the literature, with examples including the dimerization of pristine C 60 through high pressure treatment, mechanochemical synthesis using KCN and K 2 CO 3 or dipolar cycloaddition reactions . Besides the [2+2] carbon linking between the two buckyballs, typical bridging groups include oxygen and methylene units, as well as photo‐switchable azobenzenes .…”